Impact Of Ice On Hydrodynamic Performance And Load Of Podded Propulsor

In recent years,with the opening of the Arctic channel and the development of polar resources,the design and construction of ice-going ship have been paid more attention and developed rapidly.Because of the special structure,the podded propulsor can greatly improve the motility and maneuverability of the ship,which has become a common propulsion form of the ice-going ship.It is difficult to predict the hydrodynamic and ice loads of the podded propulsor because of its indirect or direct interaction with the crushed ice around the water area.Although scholars at home and abroad have carried out a lot of research work on the podded propulsor in open water,the load forecast analysis technology of the podded propulsor in ice-water mixed media has not been perfected.Foreign scholars have mainly used the model test method in this field,but domestic scholars did not carry out the relevant research.In this paper,numerical simulation and model test were used to study the hydrodynamic load of the podded propulsor under ice interference and the ice load under the milling and collision conditions of the ice-podded propulsor.Firstly,based on the RANS method,overlapping grid technology and the SST k-ωturbulence model were used to research the effect of ice on the hydrodynamic performance of the podded propulsor at different distances between podded propulsor and ice.The emphasis of analysis was on the unsteady hydrodynamic loads of propeller and pod unit,the pressure of the propeller and the pod,the flow field information between the ice and the propeller,the propeller disk,between the propeller and strut.The results show that the overlapping grid method had good applicability and reliability for solving the ice-podded propulsor interference problem.The smaller the space between the ice and propellers is,the larger the advance coefficient is,the larger the oscillation range of propeller thrust and torque is,and the more obvious the ice blockage effect on the podded propulsor is.When the blade rotates to the blockage area behind the ice,the obvious high-and low-pressure areas are generated on the blade face and blade back,which are the main reasons for the large increase of propeller thrust and torque.In view of the complexity of the navigation environment in the ice area and the limitations of the research,the numerical simulation research on the influence of ice size parameter variation on hydrodynamic performance of podded propulsor was carried out.The effects of ice length,width and thickness on the hydrodynamic performance and flow field characteristics of podded propulsor were analyzed.The influence of different sizes of ice on the hydrodynamic performance of podded propulsor was summarized,and the main reasons for the difference of hydrodynamic performance of podded propulsor were explored.The results show that the thickness of ice had the most obvious effect on the hydrodynamic performance of podded propulsor in the process of ice size parameter variation.The results of numerical simulation provide a reference for the selection of ice size parameters in the theoretical research,numerical simulation and experiment-based research of ice interacts with podded propulsor.the setup of the hydrodynamic performance of the podded propulsor in coupled research and the design of the ice class podded propulsor.Considering the different structure and complex geometry of the podded propulsor,the idea of panel method was used to discretize the propeller,strut and pod of the podded propulsor into real geometry model.Based on the peridynamic method,the contact detection algorithm of the ice-podded propulsor was proposed.According to the complexity of the navigation condition and the diversity of the structure of the podded propulsor,the discrimination methods were proposed respectively for the dynamic radial and circumferential of the contact between the propeller and ice,the contact between the ice and the strut,as well as the pod and the propeller hub.At the same time,the calculation models of propeller and ice milling conditions under the straight ahead condition,azimuthing condition and dynamic azimuthing condition have been established respectively,as well as the calculation models of ice collision with strut,pod and hub under three navigation states,which are the prediction of the ice load of the podded propulsor in ice area laid the foundation.According to the established calculation model of the milling condition of the ice-podded propulsor,the influence of the number of blade grids and the ice material spacing on the calculation results was analyzed to ensure the convergence of the calculation method,and the feasibility of the numerical method is verified by comparing the experimental values.On this basis,the change of contact load between the ice and propeller milling condition has been studied under the straight ahead condition,azimuthing condition and dynamic azimuthing condition of podded propulsor.It focuses on the analysis of the ice load on the propeller and pod unit when the parameters include ice pushing speed,milling depth,propeller rotational speed and podded propulsor azimuth angle changing.The milling process of the ice-propeller under dynamic azimuthing condition of podded propulsor is described in detail.The results show that the propeller axial force increases at first,then decreases and then increases with the increase of ice pushing speed.At the same time,the torque of propeller and pod unit increases gradually.When the podded propulsor is milling with ice in the azimuthing condition,the maximum values of the propeller axial force,the propeller blade own torque and the pod unit torque appear in different azimuth angles.The numerical model of ice-podded propulsor collision condition established in this paper has been combined with the collision characteristics of ice-podded propulsor,the change of contact load of podded propulsor when it collides with ice in the the straight ahead condition,azimuthing condition and dynamic azimuthing condition is simulated.This paper focused on the analysis of parameters such as different propeller rotational speed,different propeller rotation direction,different ice moving speed and different ice mass when the podded propulsor is in the the straight ahead condition.At the same time,the azimuthing angles and the azimuthing rates of the podded propulsor were analyzed,and the effects of ice.propeller,strut,pod and hub on the ice load of podded propulsor were obtained.The results show that when the rotational speed of the propeller is equal,the ice load of the propeller in reverse rotation is greater than that in forward rotation.Through the analysis of the ice load and the observation of the ice breaking phenomenon when the ice collides with the strut,the pod and the propeller hub under the conditions of straight ahead,azimuthing and dynamic azimuthing.the correctness of the regional contact discrimination method proposed in this paper is verified.An ice propeller milling test platform was set up in the ship model towing tank of Harbin Engineering University to measure the ice load in the process of ice-propeller milling.Firstly,the advantages and disadvantages of fresh water ice and paraffin model ice were analyzed,and paraffin model ice was selected as the research object,the variation of ice load with different model ice pushing speed,milling depth,propeller rotational speed and propeller scale were key study object.Through the analysis of the repeatability of the test results,the reliability and stability of the measurement data of the ice propeller milling test platform designed in this paper were proved.The measurement results show that the milling depth of the ice-propeller and the pushing speed of the model ice have great influence on the ice load of the propeller.The high-speed camera was used to capture the milling process of the ice-propeller,which proves the existence of the shielding effect of the blade,and provides technical support for the milling experiment of propeller and ice in the tank.